2.1. Herpes Virus Infection and Vaccine
The herpesviruses include the herpes simplex viruses (HSV), comprising two closely related variants designated types 1 (HSV-1) and 2 (HSV-2). Primary HSV infections are seldom life threatening in healthy adults, but can have severe consequences in newborns whose mothers have had a primary infection during pregnancy. HSV-1 and HSV-2 are associated in some individuals with frequent and/or painful recurrences that manifest themselves as cold sores and genital herpes, respectively. HSV is a prevalent cause of genital infection in humans, with an estimated annual incidence of 600,000 new cases and with 10 to 20 million individuals experiencing symptomatic chronic recurrent disease. Although continuous administration of antiviral drugs such as acyclovir ameliorates the severity of acute HSV disease and reduces the frequency and duration of recurrent episodes, such chemotherapeutic intervention does not abort the establishment of latency nor does it alter the status of the latent virus. As a consequence, the recurrent disease pattern is rapidly reestablished upon cessation of drug treatment. Currently there exists no effective vaccine for the prevention or treatment of HSV-1 or HSV-2.
Most of the approaches for vaccination available today have been researched for the treatment of HSV infection. Traditional ways of preparing vaccines include the use of either inactivated or attenuated pathogens. A suitable inactivation of the pathogenic microorganism renders it harmless as a biological agent but does not destroy its immunogenicity. Injection of these “killed” particles into a host will then elicit an immune response capable of preventing a future infection with a live microorganism. However, a major concern in the use of inactivated pathogens as vaccines is the failure to inactivate all the microorganisms. Even when this is accomplished, since killed pathogens do not multiply in their host, or for other unknown reasons, the immunity achieved is often incomplete, short lived and requires multiple immunizations. Finally, the inactivation process may alter the microorganism's antigens, rendering them less effective as immunogens. Several HSV vaccines derived from inactivated virions have been evaluated clinically, and proven ineffective.
Attenuation refers to the production of strains of pathogenic microorganisms which have essentially lost their disease-producing ability. Attenuated pathogens often make good immunogens as they actually replicate in the host cell and elicit long lasting immunity However, several problems are encountered with the use of live vaccines, the most worrisome being insufficient attenuation and the risk of reversion to virulence. In addition, by using live vaccines for herpes viruses, latency may be established, and thus there is the potential for reactivation-associated or other chronic disease.
An alternative to the above methods is the use of subunit vaccines. This involves immunization only with those components which contain the relevant immunological material. Because of the risks associated with inactivated and attenuated pathogens, subunit vaccines containing purified viral proteins represent a relatively safe alternative. However, previous clinical experience with HSV subunit vaccines has not been encouraging. A recent phase III trial of an HSV-2 subunit vaccine developed by the Chiron Vaccine Study Group failed to prevent or delay outbreaks in infected individuals (Corey et al, Journal of the American Medical Association 282:331-340, 1999).
An effective vaccine that eliminates or decreases the transmission of HSV-1 and HSV-2 from infected to uninfected individuals would be highly desirable.
2.2. Use of Adjuvants in Vaccines
Vaccines are often formulated and inoculated with various adjuvants. The adjuvants aid in attaining a more durable and higher level of immunity using small amounts of antigen or fewer doses than if the immunogen were administered alone. Presently, aluminum salt-based (“alum”) adjuvants are the only immunologic adjuvants used in U.S.-licensed vaccines. However, a variety of novel adjuvants which may be used to augment or replace alum in human vaccines has been under development and in preclinical and clinical evaluation for decades. Adjuvant mechanisms of action include increasing the biological or immunological half-life of vaccine antigens; improving antigen delivery to antigen presenting cells (APCs) and antigen processing and presentation by APCs; and inducing the production of immunomodulatory cytokines.
2.3. Heat Shock Proteins
Heat shock proteins (HSPs), also referred to as stress proteins, were first identified as proteins synthesized by cells in response to heat shock. HSPs have been classified into five families based on molecular weight: HSP100, HSP90, HSP70, HSP60, and smHSP. Many members of these families were found subsequently to be induced in response to other stressful stimuli including nutrient deprivation, metabolic disruption, oxygen radicals, and infection with intracellular pathogens (see Welch, May 1993, Scientific American 56-64; Young, 1990, Annu. Rev. Immunol. 8:401-420; Craig, 1993, Science 260:1902-1903; Gething et al., 1992, Nature 355:33-45; and Lindquist et al., 1988, Annu. Rev. Genetics 22:631-677). Members of the heat shock protein family include hsc70, hsp70, hsp90, hsp110, gp96, grp170, and calreticulin.
Studies on the cellular response to heat shock and other physiological stresses revealed that the HSPs are involved not only in cellular protection against these adverse conditions, but are also in essential biochemical and immunological processes in unstressed cells. HSPs accomplish different kinds of chaperoning functions. For example, members of the HSP70 family, located in the cell cytoplasm, nucleus, mitochondria, or endoplasmic reticulum (Lindquist et al., 1988, Ann. Rev. Genetics 22:631-677), are involved in the presentation of antigens to the cells of the immune system, and are also involved in the transfer, folding and assembly of proteins in normal cells. HSPs are capable of binding proteins or peptides, and releasing the bound proteins or peptides in the presence of adenosine triphosphate (ATP) or acidic conditions (Udono and Srivastava, 1993, J. Exp. Med. 178:1391-1396).
Srivastava et al. demonstrated immune response to methylcholanthrene-induced sarcomas of inbred mice (1988, Immunol. Today 9:78-83). In these studies, it was found that the molecules responsible for the individually distinct immunogenicity of these tumors were glycoproteins of 96 kDa (gp96) and intracellular proteins of 84 to 86 kDa (p84/86) (Srivastava et al., 1986, Proc. Natl. Acad. Sci. USA 83:3407-3411; Ullrich et al., 1986, Proc. Natl. Acad. Sci. USA 83:3121-3125). Immunization of mice with gp96 or p84/86 isolated from a particular tumor rendered the mice immune to that particular tumor, but not to antigenically distinct tumors. Isolation and characterization of genes encoding gp96 and p84/86 revealed significant homology between them, and showed that gp96 and p84/86 were, respectively, the endoplasmic reticular and cytosolic counterparts of the same heat shock proteins (Srivastava et al., 1988, Immunogenetics 28:205-207; Srivastava et al., 1991, Cum Top. Microbiol. Immunol. 167:109-123). Further, hsp70 was shown to elicit immunity to the tumor from which it was isolated but not to antigenically distinct tumors. However, hsp70 depleted of peptides was found to lose its immunogenic activity (Udono and Srivastava, 1993, J. Exp. Med. 178:1391-1396). These observations suggested that the heat shock proteins are not immunogenic per se, but form noncovalent complexes with antigenic peptides, and the complexes can elicit specific immunity to the antigenic peptides (Srivastava, 1993, Adv. Cancer Res. 62:153-177; Udono et al., 1994, J. Immunol., 152:5398-5403; Suto et al., 1995, Science 269:1585-1588).
Noncovalent complexes of HSPs and peptide, purified from cancer cells, can be used for the treatment and prevention of cancer and have been described in PCT publications WO 96/10411, dated Apr. 11, 1996, and WO 97/10001, dated Mar. 20, 1997 (U.S. Pat. No. 5,750,119 issued May 12, 1998, and U.S. Pat. No. 5,837,251 issued Nov. 17, 1998, respectively, each of which is incorporated by reference herein in its entirety). The isolation and purification of HSP-peptide complexes has been described, for example, from pathogen-infected cells, and used for the treatment and prevention of infection caused by the pathogen, such as viruses, and other intracellular pathogens, including bacteria, protozoa, fungi and parasites (see, for example, PCT Publication WO 95/24923, dated Sep. 21, 1995). Immunogenic stress protein-antigen complexes can also be prepared by in vitro complexing of stress protein and antigenic peptides, and the uses of such complexes for the treatment and prevention of cancer and infectious diseases has been described in PCT publication WO 97/10000, dated Mar. 20, 1997 (U.S. Pat. No. 6,030,618 issued Feb. 29, 2000). The use of stress protein-antigen complexes for sensitizing antigen presenting cells in vitro for use in adoptive immunotherapy is described in PCT publication WO 97/10002, dated Mar. 20, 1997 (see also U.S. Pat. No. 5,985,270 issued Nov. 16, 1999).